Selective growth of stacked InAs quantum dots by using the templates formed by the Nano-Jet Probe
Introduction
The control of the nucleation site of quantum dots (QDs) is one of the key issues in the nanoscale design of optoelectronic functional QD devices [1], [2]. Recently, we have proposed a new nano-probe-assisted technique that enables the formation of site-controlled (SC) InAs QDs [3]. By using a specially designed atomic-force-microscope (AFM) cantilever referred to as the Nano-Jet Probe (NJP), two-dimensional (2D) arrays of ordered indium (In) nano-dots are reproducibly fabricated on a GaAs substrate [4]. These In nano-dots are directly converted into InAs arrays by the subsequent irradiation of arsenic flux using the droplet epitaxy technique [5], [6]. However, the quality of these fabricated InAs QDs is not very good since the photoluminescence (PL) emission from the QDs could not be obtained at room temperature. This is probably due to the following reasons. The first reason is the contamination of In, which is charged in the NJP. At present, In is charged in a separate vacuum system and the NJP is introduced into the QD fabrication system through air. Therefore, In, which is one of the constituents of InAs QDs, probably contains oxygen. Another possibility is the low-temperature process during the crystallization of the In nano-dots. Droplet epitaxy is a method for obtaining the crystals of compound semiconductors by annealing one of the melted materials in the vapor of the other materials at low temperatures, and it is attributed to the VLS mechanism [7]. Therefore, there is a possibility that the defects produced by this low-temperature technique result in a nonradiative center in the crystallized InAs QDs. However, the results mentioned in previous papers indicate that we obtained the InAs dots, although their quality is insufficient. Therefore, we decided to use the fabricated InAs QDs as a strain template for the stacking of the QDs. In this paper, we report on the results of the stacked SC-QDs fabricated by using the strain templates formed by the NJP method. The optical property of the fabricated stacked QDs is also reported.
Section snippets
Experimental
Fig. 1 shows the schematic illustrations of the experimental procedures. First, by using the NJP, we fabricated 2D In nano-dot arrays (Fig. 1(a)). Experiments involving the In nano-dot formation were performed using a conventional non-contact ultra-high vacuum (UHV)-AFM system operating at room temperature. The cantilever was a piezoelectric type with a hollow pyramidal tip made of silicon nitride, which has a micro-aperture at the apex and an In-reservoir tank within the stylus. By applying a
Results and discussions
We measured the optical property of the abovementioned stacked QD array. A selective grown area was excited using a He–Ne laser (λ = 633 nm) with an optical microscope; here, the size of the focal point on the sample was a few square microns and the excitation power was ∼0.5 mW. Fig. 3 shows the microprobe-PL mapping of the stacked InAs SC-SKQDs measured at room temperature. This image was obtained by plotting the output of an InGaAs CCD detector, which was accumulated in the wavelength range of
Summary
We have demonstrated the fabrication of the stacked InAs SC-SKQDs. Starting with the fabrication of the regular SC-QD arrays by the NJP method, we vertically aligned the SK-QDs by the strain-induced stacking method, thereby producing stacked SC-SKQD structures. The PL measurements reveal the good crystallographic quality of the stacked QD structures. Further improvements in the initial SC-QD array and growth conditions will increase the possibility of achieving a uniform QD size. This method
Acknowledgement
This work was supported by the New Energy and Industrial Technology Development Organization (NEDO) Project.
References (8)
- et al.
Physica E
(2004) - et al.
Thin Solid Films
(2004) - et al.
Physica E
(2008) - et al.
Phys. Rev. Lett.
(1999)
Cited by (4)
Site-controlled InAs quantum dot formation grown on the templates fabricated by the Nano-Jet Probe method
2009, Journal of Crystal GrowthIn-situ STM study of MBE growth process
2019, Molecular Beam Epitaxy: Materials and Applications for Electronics and OptoelectronicsMaterials for nanophotonics
2017, Optical Materials and ApplicationsTemperature-Dependent Site Control of InAs/GaAs (001) Quantum Dots Using a Scanning Tunneling Microscopy Tip During Growth
2010, Nanoscale Research Letters